The present invention relates to a bidirectional rotational speed control system for motors, profitably employed for controlling either the forward or the backward speed of the magnetic medium in magnetic recording equipments or magnetic tape transport units.
It is known that, in such units, the magnetic tape is driven by either a driving roller or a single capstan, over the periphery of which the tape is partially wound or against which the magnetic tape is pressed by a pressure roller.
The capstan is driven by a motor controlled by a proper regulating circuit. In U.S. Pat. No. 3,740,633 a frequency to voltage transducer is described, which is particularly useful in obtaining precise information on the rotational speed, and to supply a proper feedback signal which may be used in a control circuit. A complete regulation system is schematically represented, as an example, in FIG. 1 of said patent. In U.S. Pat. No. 3,745,436 a regulation system for a magnetic tape unit provided with such a transducer device is described. In particular, to obtain a "bidirectional" speed control, that is in the forward and backward direction, it was required to employ two different transducer devices which delivered, respectively, a positive voltage signal and a negative voltage signal, selectively applied to an amplifier circuit. Such a control system is represented, as a simplified block diagram, in FIG. 3 of said U.S. Pat. No. 3,745,346 and in the present patent application the prior art represented by such FIG. 3 of the patent is incorporated as FIG. 1.